Add branch alias

Author: barryvdh

README.md

@@ -15,7 +15,7 @@ Omnipay is installed via [Composer](http://getcomposer.org/). To install, simply
 to your `composer.json` file:
 
 ```
-composer require omnipay/braintree
+composer require omnipay/braintree:"~2.0@dev"
 ```
 
 ## Basic Usage

composer.json

@@ -36,5 +36,10 @@
     },
     "require-dev": {
         "omnipay/tests": "~2.0"
+    },
+    "extra": {
+        "branch-alias": {
+            "dev-master": "2.0.x-dev"
+        }
     }
 }